The TS440 power amplifier is a push-pull amplifier with a very low output impedance.
To make a conversion to 50 ohms, a 1/16 impedance transformer is used.
The secondary consists of four windings (blue wire).
The primary consists of two tubes that are connected at the top (left picture) and where the power supply for the output transistors is provided. The bottom (right picture) goes to the respective collectors of Q4 and Q5.
For measurement purposes a resistor of 3 Ohms is connected to this point.
Measurement results:
1) Without compensation:
2) With 1.500 pF compensation:
3) With 1.300 pF compensation:
4) With 1.100 pF compensation:
